Basic boards's problem with benchmark_tx.py/benchmark_rx.py

hello,everyone!

I have tested my usrp boards Basic Tx/Basic Rx, and run the following
commands:
Basic Tx: python benchmark_tx.py -f 100M
Basic Rx: python benchmark_rx.py -f 100M

It seemed that both sides send or receive ok spearately, but there is
no link constructed between them, and I have tried it with different
kinds of antenna but all couldn’t receive properly, so does anyone know
the reason and what could be?

BTW,I have successfully test daughterboards RFX2400 within the same
scene and the same program, just work in different frequency,but one
success and the other failure.